Diffuse γ -ray emission near the young massive cluster NGC 3603

Abstract

We report the detailed analysis of Fermi Large Area Telescope's data towards the direction of the young massive star cluster NGC 3603. The emission shows a hard spectrum with a photon index of 2.3 ± 0.1 from 1 GeV to 250 GeV. The spatial correlation with the ionised gas indicates a hadronic origin. The total cosmic ray (CR) protons energy budget is estimated to be of the order of 1050 erg assuming the γ-rays are produced in the interaction of CRs with ambient gas. The environment and spectral features show significant similarity with the GeV emission seen from the Cygnus cocoon. The emission can be produced by a pulsar wind nebular or by the super bubble associated with the young star clusters. In the latter case, it further establishes that young star clusters may be a γ-ray source population and that they can potentially accelerate a significant fraction of the Galactic cosmic rays.